PXE: if a board has set its own value for CONFIG_BOOTP_VCI_STRING do not set the default one. Use the board set value instead

Signed-off-by: Dennis Gilmore <dennis@ausil.us>
diff --git a/include/config_distro_defaults.h b/include/config_distro_defaults.h
index bd8fbca..d8165cc 100644
--- a/include/config_distro_defaults.h
+++ b/include/config_distro_defaults.h
@@ -23,12 +23,18 @@
 #if defined(__arm__) || defined(__aarch64__)
 #define CONFIG_BOOTP_PXE_CLIENTARCH     0x100
 #if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__)
+#if !defined(CONFIG_BOOTP_VCI_STRING)
 #define CONFIG_BOOTP_VCI_STRING         "U-boot.armv7"
+#endif
 #elif defined(__aarch64__)
+#if !defined(CONFIG_BOOTP_VCI_STRING)
 #define CONFIG_BOOTP_VCI_STRING         "U-boot.armv8"
+#endif
 #else
+#if !defined(CONFIG_BOOTP_VCI_STRING)
 #define CONFIG_BOOTP_VCI_STRING         "U-boot.arm"
 #endif
+#endif
 #elif defined(__i386__)
 #define CONFIG_BOOTP_PXE_CLIENTARCH     0x0
 #elif defined(__x86_64__)